Many layers of dielectric films are used to make an integrated circuit. IC manufacturing requires dielectric films to have certain properties in order for the circuit to function as designed. For example, there is a general need for materials with low dielectric constants (low-k). Using low-k materials as the intermetal dielectric (i.e., the layer of insulator separating consecutive levels of the conductive metal interconnects) reduces the delay in signal propagation due to capacitive effects, otherwise know as the RC delay. A dielectric material of low dielectric constant will have low capacitance, and hence the RC delay of an IC constructed with such a material will be lower as well.
In addition to low dielectric constants, certain material properties may be specified. The semiconductor manufacturing processes, with all the temperature changes, mechanical polishing, cutting, and packaging, impose a lot of stress onto the semiconductor. To avoid premature device failure, the film should not be damaged by subsequent manufacturing process. Some devices may specify a certain hardness, for example.
As another example, there is a general need for materials with specific tensile or compressive stresses. A layer of tensile material may be used between compressive material to reduce or avoid wafer warping. These and other properties may be met on the film as deposited, or after treatment.
One such treatment may be a thermal process in which the substrate is heated to a temperature for a time. A thermal treatment may remove unwanted particles from the film, or change its stresses or other properties. These thermal processes, however, have certain difficulties. In particular, substrate temperatures generally need to be high (i.e., greater than about 400 or 500 degrees Celsius or much higher) with exposure times typically on the order of many hours. The long exposure time may be unsuitable for mass manufacturing. These conditions may also damage copper containing devices, especially in when a low-k dielectric is being cured. Also, the use of temperature sensitive materials may limit the temperature and or duration of exposure, e.g., nickel silicide precludes inducing film stress by using temperatures above 400° C. and some SiN films allow a cure temperature up to 480° C.
To overcome these disadvantages of thermal processing, another technique has been developed, which involves exposing the film to UV radiation. Irradiation of the low-k permits modulation of desired film properties such as dielectric constant or film stress at lower temperatures. The film properties obtained are strongly affected by the UV curing process and conditions.
What are needed therefore are improved methods and devices for treating dielectric films with UV radiation to obtain desired film properties.